This invention relates generally to a machine for fabricating metal duct or pipe from a continuous, thin metal strip which is corrugated along its longitudinal axis, helically wound and interlocked along adjacent lateral edges to form a substantially circular, bendable metal duct. Helically wound metal duct has been widely utilized in recent years for the transport of hot and cold air in commercial and industrial applications. There have been many problems associated with mass production of the duct, some of which include the sensitivity of a thin metal strip to wrinkling or buckling during corrugation and in the positioning of the strip edges to expeditiously interlock adjacent lateral edges in a helically wound cut to insure a continuous, secure, interlocked seam. Many of the devices shown in the prior art for accomplishing the fabrication of such helically wound metal duct have proven to be quite slow in operation, unreliable and subject to stoppages which interrupt the continuous manufacture of the pipe. Additional problems have arisen in the cutting of the continuously formed duct at a desired length without slowing down the duct production.
The instant invention provides a machine for the manufacture of helically wound thin duct or pipe which greatly improves the efficiency of operation and the speed of manufacture and fabrication while increasing the reliability of the machine, the machine being subject to less production stoppages. These objectives are obtained by providing a duct forming machine in which all stages of fabrication are synchronized together from a common drive means to insure uninterrupted operation. Secondly, the corrugating roller die stands include progressively larger diameter rollers between stands which create a slight pull on the foil strip as it emerges from each succeeding roller die stand while being corrugated. The pulling force acts to prevent wrinkling or buckling of the thin metal strip as it passes through the corrugating roller die stands. The corrugating rollers further act to deform the lateral edges perpendicular to the plane of the strip to prepare them for seam interlock. The longitudinal corrugations in the strip are utilized with roller guides to direct the strip in a helical path to align adjacent lateral edges preparatory to forming the interlocked seam. The seam itself is formed by passing adjacent strip edges through a pair of tucking fingers which overlaps and interlock the edges together forming a seam which is then compressed with a ridge and furrow pattern.
The device includes a cam-actuated travelling, rotary saw that moves parallel to the longitudinal axis of the formed pipe at the same forward speed as the pipe during cutting. The saw blade is adjustable relative to the longitudinal axis of the formed duct to accomodate the cutting of duct of different diameters.